Study Of The Hole Transport Properties Of P-type Metal Oxides

In recent years,halide perovskite solar cells（PSCs）have received more and more attention due to their excellent power conversion efficiency（PCE）.In just over a decade,its certified PCE has soared from 3.8%to 25.7%,mainly due to the superior photoelectric properties of halide perovskite materials,such as high light absorption coefficient,low exciton binding energy,high carrier mobility and long carrier life.In inverted structured PSCs,the hole transport layer（HTL）plays the role of transporting holes and blocking electrons,which affects the PCE of PSCs.Therefore,the selection of a suitable HTL contributes to the device performance.In this thesis,we mainly study the interfacial properties between the nickel cobaltate（NiCo₂O₄）and the perovskite layer.The performance of PSCs is improved by Mg doping NiCo₂O₄ HTL and graphene oxide（GO）to improve hole extraction/transport,optimize energy level sequence and improve crystallization of perovskite films.The main research and results are as follows:（1）Magnesium（Mg）was chosen to dope NiCo₂O₄ HTL and the doping effect on the performance of PSC were studied.Compared with the undoped NiCo₂O₄ film,slight doping of Mg can improve the conductivity and hole mobility of NiCo₂O₄ film.The density functional theory revealed that the electronegativity of Mg is higher than of Nickel（Ni）,and the electron transfer of Mg to Oxygen（O）is more than that of Ni.The low concentration of Mg doping can improve the density of electron states at the Fermi level of NiCo₂O₄,and then increase the hole concentration of NiCo₂O₄.Compared with the undoped PSCs,the device PCE was improved from 14.07%to 16.71%,J_sc(Short Circuit Current Density,J_sc)from 19.81 m A/cm~2 to 21.92 m A/cm~2,V_oc(Open Circuit Voltage,V_oc)from 0.95 V to 0.99 V,and FF（Fill Factor,FF）from 74.44%to 76.99%after 5%mol Mg doping.The results show that Mg doped NiCo₂O₄ HTL is an effective strategy to improve the performance of PSCs.（2）Interface recombination is one of the main factors affecting device performance and stability in PSCs,and interface modification is an effective strategy to solve this problem.In this work,by using GO as an interface modification layer on Mg:NiCo₂O₄,the grain uniformity of perovskite film on Mg:NiCo₂O₄ was promoted and the microstrain of perovskite film was reduced.The introduction of GO interface layer promotes the crystallization of perovskite film and improves the ultraviolet absorption of the film,reduces the defects of perovskite,and improves the ability of hole extraction/transfer.Compared with the unmodified device（16.49%）,the device achieved a maximum PCE of 18.05%.In addition,the device with GO modification showed higher stability.